In foam-cutting machines, the horizontally, vertically or basically randomly oriented cutting tool produces displacement forces in the workpiece to be cut upon entering the foam and also during cutting. The forces are produced, among other things, by the friction between the tool and the foam as forces in the oscillation and/or cutting channel longitudinal directions as well as by the wedging effect of the tool acting as sliding forces in the advancing direction. Both force directions are oriented substantially perpendicular to each other. The forces produce at least local shifts of the foam, which ultimately result in inaccuracies of the cut line. The extent of the shift depends on different factors, including the material properties of the workpiece and the geometric configuration of the blade of the tool. Due to the operating principle, shifts in the upper region of the loose foam block are greater than in the lower region close to the contact location on the table. This is due to the fact that the table guides the foam, which in the region of the interface between the foam and table under high friction results in very accurate positioning and accordingly small shifts. The further away from the boundary layer the cut is made, the less the effect of the counter-pressure of the table, which means that the shifts increase with increasing distance from the table.
So as to counteract these shifts, a pressure pad is engaged with the foam, which with respect to the shifts has a similar effect as the table beneath the foam. This pressure pad is referred to as a hold-down device.
Thus hold-down devices in foam-cutting machines are known. They are used to clamp the foam block or a foam-plate stack between the table and the hold-down device in order to stabilize and steady the material on the table enough so that during cutting, particularly during contour cutting, the material block experiences minimal deflection by the cutting tool and/or minimal inherent vibration, thus allowing exact contour cuts.
Cutting machines with hold-down devices have been developed that are connected directly to the table and comprise hold-down plates held in a frame. This design makes the table very heavy, which is disadvantageous for the acceleration response of movable tables. Furthermore, the high frame may result in undesirable vibrations while advancing during the cut, which in turn negatively influence cutting accuracy. These cutting machines comprise a center support that shortens the free bending length of the blade that depending on the extent of shortening results in significantly reduced bending of the cutting tool. This largely reduces cutting tolerances that are a function of the operating principle and result from the bending of the cutting tool. If with such a cutting machine the center support needs to be moved into a position more favorable for cutting, the hold-down plates located in the travel path have to be removed from the frame and reinstalled in the new location after displacement of the center support. This process is cumbersome and particularly time-consuming.
For this reason, hold-down devices have been proposed that are provided with hold-down rollers. The hold-down devices are mounted on the machine frame so that their height is adjustable. The rollers, at least in the region of the center support, are spaced apart to ensure that the center support can be displaced transversely without difficulty. The disadvantage with hold-down rollers, however, is that the soft material blocks are not sufficiently supported, at least when it comes to some cutting applications. Instead of surface contact of the hold-down device, the rollers only have line contact. The soft material cannot be held down between the rollers. In the event of complicated contour cuts, this small contact surface may result in scrap during cutting.